#8341: detect_poles doesn't find a vertical asymptote where both sides go to
infinity
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Reporter: jason | Owner: was
Type: defect | Status: new
Priority: major | Milestone: sage-4.3.4
Component: graphics | Keywords:
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Changes (by robert.marik):
* cc: robert.marik (added)
Comment:
It would be nice to fix this. But current detect_poles simply skips the
lines with slope close to pi/2 and draws the vertical asyptote, if the
function changes sign (skips from -infinity to +infinity). I think that
using this idea it is not possible to detect vertical asymptote.
Just some attempts: If we drop the condition which requires change in
sign,
we get "interval of asymptotes" - the asymptote is too thick.
Making epsilon smaller introduces problems with other graphs.
This is the diff with my experiments, if someone is interested
{{{
diff -r a1d167a37d52 sage/plot/plot.py
--- a/sage/plot/plot.py Thu Feb 25 13:42:16 2010 -0600
+++ b/sage/plot/plot.py Sat Mar 06 15:23:11 2010 +0100
@@ -2698,17 +2698,16 @@
x0, y0 = exclude_data[i]
x1, y1 = exclude_data[i+1]
# detect poles
- if (not (polar or parametric)) and detect_poles != False \
- and ((y1 > 0 and y0 < 0) or (y1 < 0 and y0 > 0)):
+ if (not (polar or parametric)) and detect_poles != False:
# calculate the slope of the line segment
dy = abs(y1-y0)
dx = x1 - x0
alpha = (RDF(dy)/RDF(dx)).arctan()
- if alpha >= RDF(pi/2) - epsilon:
+ if alpha >= RDF(pi/2) - 0.00001:
G += line(data[start_index:i], **options)
if detect_poles == 'show':
# draw a vertical asymptote
- G += line([(x0, y0), (x1, y1)], **pole_options)
+ G += line([(x0, -1e100), (x1, 1e100)],
**pole_options)
start_index = i+2
}}}
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/8341#comment:1>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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